J . Am. Chem. Soc. 1993, 115, 2808-28 17
2808
Synthesis of Cyclic Bifunctional Organomagnesium Compounds. X-ray Crystal Structures of Tetrameric Organomagnesium Clusters+*$ Marcus A. G. M. Tinga,§ Gerrit Schat,§ Otto S. Akkerman,§ Friedrich Bickelhaupt,',§ Ernst H o m , I Huub Kooijman,I Wilberth J. J. Smeets,I and Anthony L. Spekl Contribution from the Scheikundig Luboratorium, Vrije Universiteit. De Boelelaan 1083, NL- 1081 H V Amsterdam, The Netherlands, and Vakgroep Kristal- en Structuurchemie, Rijksuniversiteit Utrecht, Padualaan 8 , NL-3584 CH Utrecht, The Netherlands Received November 3, 1992
Abstract: Three cyclic bifunctional organomagnesium compounds were prepared by three different routes. Reaction of 1,8-dibromo- or 1,8-diiodonaphthalene with metallic magnesium gave the corresponding di-Grignard reagents 3, from which the halide-free 1,8-naphthaIenediylmagnesium(4) was isolated. o-Phenylenemagnesium (10) was prepared by transmetalation from o-phenylenemercury with magnesium. The reaction of freshly sublimed magnesium with diphenylacetylene gave a mixture of cis- and trans-diphenylvinylenemagnesium;cis-diphenylvinylenemagnesium(15) was isolated by crystallization from THF. The X-ray crystal structures of 4, 10, and 15 showed these compounds to be tetrameric in the solid state. Crystal data are as follow: 4, C56H&g404.5C4H80, tetragonal, space group 1 4 , / a , with cell dimensions a = 14.429(2) and c = 34.927(4) A, final R = 0.068, R , = 0.083; 10, C4&8Mg&4, monoclinic, space group 12/a, with cell dimensions a = 17.071(3), b = 11.877(1), and c = 18.809(1) A, @ = 99.97(1)O, final R = 0.066, R , = 0.092; 15, C72H72Mg404-2C4H80, tetragonal, space group P&?,c, with cell parameters a = 17.464(1) and c = 11.91 l(2) A, final R = 0.067, R , = 0.089. Their cores consist of distorted tetrahedrons of magnesium atoms. Each organic fragment is positioned above the face of such a tetrahedron and is bonded to three magnesium atoms via two carbon atoms. One carbon is single-bonded to a magnesium, and the other bridges two magnesiums by a 3-center, 2-electron bond. Each magnesium atom in the three structures has a pseudotetrahedral coordination; it is coordinated to one single-bonded and two bridging carbon atoms and a T H F molecule. The arrangement of four organic groups over the four faces of a magnesium tetrahedron can be of either C2 or of S4symmetry. Compounds 4 and 15 were found to have S4 symmetry, whereas 10 has C2 symmetry. Introduction For some time we have been engaged in an investigation of bifunctional organomagnesium compounds. The results of this work and that of other groups in this field have been reviewed.' Investigations on the structure of bifunctional organomagnesium compounds have been hampered by several factors. First of all, the extreme sensitivity of these compounds toward air necessitates the use of special equipment and techniques. A second problem is posed by the Schlenk equilibrium, which, schematically and in its simplest form, is represented for bifunctional organomagnesium compounds in Scheme I, as it relates di-Grignard reagents A to cyclic bifunctional organomagnesium compounds B. The Schlenk equilibria of di-Grignards have been evaluated in several cases.2 In solution, many additional equilibria involving association and/or exchange of the substituents at magnesium (organic rest, halogen) are operative. All these equilibria are generally very fast at room temperature. This leads to a complicated dynamic situation. The situation is much simpler with cyclic organomagnesium compounds. Of the equilibria mentioned for Grignard reagents, ' Dedicated to Prof. Dr. U. Schollkopf on the occasion of his 65th birthday. 1
Part of this work has been reported as a communication: Tinga. M. A.
G. M.; Akkerman, 0.S.; Bickelhaupt, F.; Horn, E.; Spek, A. L. J . Am. Chem. Soc. 1991, 113, 3604.
Vrije Universiteit. University of Utrecht. ( 1 ) (a) Bickelhaupt, F. Angew. Chem. 1987. 99, 1020. (b) Bickelhaupt. +
I
F. Pure Appl. Chem. 1990, 62, 699. (2) (a) Holtkamp, H. C.; Blomberg. C.; Bickelhaupt, F. J . Organomet. Chem. 1969, 19, 279. (b) Holtkamp, H. C.; Schat, G.; Blomberg, C.; Bickelhaupt, F. J . Organomet. Chem. 1982,240, I . (c) Freijee. F. J . M.; Van der Wal, G.; Schat, G.; Akkerman, 0. S.;Bickelhaupt. F. J . Orgonomet. Chem. 1982, 240, 229. (d) Markies, P. R.; Altink. R . M.; Villena, A,; Akkerman,O. S.;Bickelhaupt. F.;Smeets,W. J . J.;Spek. A. L. J . Organomet. Chem. 1991, 402, 289.
only association is relevant, and as the exchange of the carbon anion (Le., the organic rest) is usually rapid, the system will always adopt the thermodynamically favored degree of association. Some cyclic bifunctional organomagnesium compounds have been isolated and investigated by X-ray crystal structure determinations. Their structures were found to be m o n o m e r i ~ ,d~i ~m.e~r i ~ , ~ or trimeric5 In all these compounds, thenumber of carbon atoms separating two magnesium atoms is four or higher. Cyclic bifunctional organomagnesium compounds with less than four carbon atoms separating both magnesiums are virtually insoluble in T H F and are therefore assumed to be polymeric.6 Their poor solubility prevented structural characterization. We now present the synthesis and structure of three cyclic bifunctional organomagnesium compounds in which the number of carbon atoms separating both magnesium atoms is two or (3) (a) Lehmkuhl, H.; Shakoor, A.; Mehler, K.; Kriiger, C.; Angermund, K.; Tsay, Y. H. Chem. Ber. 1985,118,4239. (b) Bogdanovic, B.; Janke, N.; Kriiger, C.; Mynott, R.; Schlichte, K.; Westeppe, U. Angew. Chem. 1985.97, 972. (c) Alonso, T.; Harvey, S.;Junk, P. C.; Raston, C. L.;Skelton, B. W.; White. A. H . Organometallics 1987,6, 21 IO. (d) Bogdanovic, B.; Janke, N.; Kriiger. C.; Schlichte, K.; Treber, J. Angew. Chem. 1987, 99, 1046. (e) Engelhardt, L . M.; Harvey, S.; Raston, C. L.; White, A. H. J . Organomet. Chem. 1988,341.39. ( 0 Kai,Y.;Kanehisa,N.;Miki,K.;Kasai,N.; Mashima, K.; Yasuda, H.; Nakamura, A. Chem. Lett. 1982, 1277. ( 4 ) (a) Vallino, M. Thesis, Universitt Paris VI, 1972. (b) Spek. A. L.; Schat. G.; Holtkamp. H. C.; Blomberg, C.; Bickelhaupt, F. J . Orgonomet.
Chem. 1977. 131. 331. (5) Lappert, M. F.; Martin. T. R.; Raston. C. L.; Skelton, B. W.; White, A. H. J . Chem. SOC.,Dalton Trans. 1982. 1959. (6) (a) Seetz. J. W. F. L.; Akkerman, 0.S.; Bickelhaupt, F. Tetrahedron Lett. 1981, 22, 4857. (b) Seetz, J. W. F. L.; Hartog, F. A,; Bohm, H. P.; Blomberg. C.; Akkerman, 0.S.; Bickelhaupt, F. Tetrahedron Lett. 1982, 23, 1497. (c) Bruin, J. W.; Schat, G . ; Akkerman, 0.S.; Bickelhaupt, F. Tefrahedron Left. 1983. 24. 3935. (d) Bruin, J. W.; Schat, G.; Akkerman, 0. S.; Bickelhaupt. F. J . Organomet. Chem. 1985, 288. 13. (e) De Boer, H. J. R ; Akkerman. 0. S.; Bickelhaupt, F. I n Organomera(licSynfhesis; Eisch, J. J.. King. R. B., Eds.; Elsevier: New York, 1988; Vol. 4, p 396.
OOO2-7863/93/1515-2808$04.00/0 0 1993 American Chemical Society
Cyclic Biftnctional Organomagnesium Compounds
J . Am. Chem. SOC.,Vol. 115, No. 7, 1993
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Scheme I11
Scheme I
D
D
U
D20 5
B
A
MqSnCI,
Scheme I1 6
2
3
4
a : X =Br: b : X = I
three. All magnesium-bonded carbon atoms in these compounds are sp2 hybridized.
Results and Discussion Several methods of preparing bifunctional organomagnesium compounds are available. The most important of these is the reaction of an organic dihalide with magnesium (direct synthesis); it results in the formation of a di-Grignard reagent or, more exactly, a solution having the formal composition of a di-Grignard reagent. Cyclic organomagnesium compounds can be obtained by three general methods: (A) conversion of a di-Grignard reagent into a cyclic organomagnesium compound by manipulation of the Schlenk equilibrium; (B) transmetalation of a cyclic organomercury compound with metallic magnesium; and (C) reaction of metallic magnesium with unsaturated molecules. Synthesis of 1,8-Naphthalenediylmagnesium. Research on 1,8dimetalated naphthalenes has been confined essentially to 1,8dilithionaphthalene (1). It was first described by Letsinger et al. in 1962' and can be prepared in two ways: treatment of 1,8dihalonaphthalenes 2 with n-b~tyllithium~ or reaction of l-bromonaphthalene with n-butyllithium, followed by a regioselective metalation using n-BuLi-TMEDA.6 Reagent 1 has proved to be useful for the synthesis of 1,8-disubstituted naphthalenes; both and organometallicIO derivatives have been obtained. In contrast, little attention has been paid to the corresponding organomagnesium compounds: the di-Grignard reagent 3 or the corresponding diarylmagnesium 1,8-naphthalenediyImagnesium (4), which are related by the Schlenk equilibrium (Scheme 11). To our knowledge, there is only one brief mention by Schechter et al. of 3b (X = I) as an alternative to 1 in the synthesis of 1H-cyclobuta[de]n a ~ h t h a l e n e . ~ Compound 4 was obtained by the general method A (vide supra). Reaction of 1,8-dibromonaphthalene (2a) with magnesium in T H F solution overnight at room temperature led to the formation of 3a. The yield, 90%, was determined by hydrolysis followed by titration of the liberated base with HC1 and of Mg2+ with ethylenediaminetetraacetic acid (EDTA);' I the observed 1:l ratio of [OH-] and [Mg2+]is usually a good indication of a Grignard reagent (RMgX). This analysis, however, does not (7) Letsinger, R. L.; Gilpin. J. A,; Vullo, W. J . J . Org. Chem. 1962, 27, 672. (8) (a) Neugebauer, W.; Clark, T.; Schleyer. P. v . R. Chem. Ber. 1983, 116, 3283. (b) Brandsma. L.; Verkruijsse, H. D. In Preparatiue Polar Organometallic Chemistry; Springer-Verlag: Heidelberg. 1987: Vol. 1, pp 195-1 97. (9) Yang, L.S.;Engler, T. A.; Shechter, H . J . Chem.Soc., Chem. Commun. 1983, 866. (IO) (a) Yang, L. S . : Shechter. H. J. Chem. Soc.. Chem. Commun. 1976, 775. (b) Meinwald. J.; Knapp. S.;Tatsuoka, T. Tetrahedron Lett. 1977, 26, 2247. (c) Seyferth, D.; Vick. S. C. J . Orgonomet. Chem. 1977, 141, 173. (d) Schmidbaur, H.; Oiler, H.-J.; Wilkinson. D. L.; Huber, B.; Muller, G . Chem. Ber. 1989, 122, 3 I . ( I I ) Vreugdenhil. A . D.; Blomberg. C. R e d . Trac. Chim. Pays-Bas 1963. 82, 453.
give any information on the Occurrence and position of the Schlenk equilibrium. Its establishment follows from the isolation of crystals of 4 upon cooling of the T H F solution of 3a. Hydrolysis of these crystals and titration with HCl and EDTA gave a ratio of 2:l for [OH-]:[Mg2+] as required for a diarylmagnesium species. When 1,8-diiodonaphthalene (2b)was reacted with magnesium in THF at room temperature, a colorless precipitate formed immediately. The precipitate, which was isolated and shown to be magnesium iodide by titration, covered the magnesium surface and thus hindered the progress of thereaction. The THFsolution contained 4, as shown by titration, and unreacted 2b;in order to drive the reaction to completion, it was necessary to add fresh magnesium and continue stirring. A better way of preparing 4 from 2b and magnesium is to perform the reaction in 2-methyltetrahydrofuran (2-MeTHF). Under these conditions, a precipitate was not formed and the di-Grignard 3b was obtained in 90% yield. Evaporation of the solvent gave an oily residue, which on addition of T H F gave a precipitate of magnesium iodide; it was separated from the solution of 4 by filtration. Recrystallization of 4 from T H F gave the pure compound. In addition to hydrolysis and titration, 4 was chemically characterized by reaction with deuterium oxide, which gave [ 1,82H2]naphthalene (5) in quantitative yield, and with chlorotrimethylstannane, which gave 1,8-bis(trimethylstannyl)naphthalene (@Ioc in low yield (22%) (Scheme 111). The main product in this latter reaction after hydrolytic workup is 1-(trimethylstannyl)naphthalene,suggesting that the incorporationof a second trimethylstannyl group at a peri position is difficult, probably due tosteric congestion. The IH and I3CN M R spectra of 4 (vide infra) were in accord with the assigned structure. The synthesis of 4 described above is a good illustration of general method A; differences in the solubilities of the three species involved in the Schlenk equilibrium are used to obtain 4 in a pure form. Synthesis of ePhenylenemagnesium. The direct synthesis of 1,2-di-Grignard reagents of benzene by reacting dihalobenzenes with magnesium is feasible, although the formation of benzyne is always a more or less prominent side reaction.I2 Under certain circumstances, such di-Grignards have been obtained in 2 0 4 0 % yields. I 3.14 Transmetalation reactions were found to give better results. The synthesis of 1,2-bis(bromomagnesio)benzene ( 9 ) , the diGrignard analogue of o-phenylenemagnesium (lo), has been reported by Wittig and Bickelhaupt; o-phenylenemercury (7) was converted by transmetalation to 1,2-dilithiobenzene (8), which, upon reaction with magnesium bromide, gave 9 (Scheme IV).'~ In analogy to the transformation 7 8, we have prepared o-phenylenemagnesium (10) by reacting 7 with metallic magnesium in T H F (Scheme V); this is an illustration of the general method B (vide supra). The progress of this reaction was monitored by the disappearance of the sparingly soluble 7. After
-.
(12) Wittig, G . Angew. Chem. 1957, 69, 245. (13) Hart, F. A.; Mann, F. G. J . Chem. SOC.1957, 3939 and references cited therein. (14) Akkerman, 0. S., unpublished results. ( 1 5 ) Wittig, G.; Bickelhaupt, F. Chem. Ber. 1958. 91, 883.
2810 J . Am. Chem. SOC.,Vol. 115, No. 7, 1993
Tinga et al.
Scheme IV
7
8
9
Scheme V
2
c12
C13
'3
L
L
10
1
Scheme VI PhCICPh 13
& THF, - 1 a l ~ C
Figure 1. Plutondrawingof the molecular structureof4, with theadopted atom labeling. Hydrogen a t a x were omitted for clarity.
[pF:g]
phHph + /Mg
1s
16
C15 C14
1D*O
phXph D D p;M; +
cis-14
trans-14
2 weeks of being stirred at room temperature, the resulting clear, brownish solution was carefully decanted from the finely divided amalgam to give 10 in 85% yield; crystallization from T H F gave 10 in 68% isolated yield. The compound was identified by its IH and I3CNMR spectra (videinfra), which were in accordance with the assigned structure. Chemical derivatization with deuterium oxide or chlorotrimethylstannane yielded [ 1,2JH2]benzene (11) or 1,2-bis(trimethylstanny1)benzene (12),16 respectively. Synthesis of Diphenylvinylenemagnesium. An example of the addition of magnesium to unsaturated organiccompounds (general method C) is the reaction of magnesium with diphenylacetylene (13). Theanalogousreactionoflithiumwith13 haskmdescribed by Szwarc et al., who observed that at -78 OC in THF, the dilithium adduct of 13 is formed." In our experience, unactivated sublimed magnesium in T H F does not react with 13, neither at room temperature nor under reflux. Activation with 1,2-dibromoethane or iodine did not result in the formation of the desired organomagnesium compound either. When magnesium was sublimed into a solution of 13 in T H F at -100 OC in an apparatus designed after Kiindig and Perret,Is a reaction did occur. After the reaction mixture had been allowed to warm to room temperature, a dark brown solution containing a yellow precipitate was obtained. Reaction of an aliquot of the total reaction mixture with deuterium oxide yielded both cis-14 and trans-14 in a 3:2 ratio, indicating the formation of both cis-( 15) and trans-diphenylvinylenemagnesium (16) (Scheme VI). The solution was decanted from the precipitate. Apparently, it contained mainly the better soluble 15, because on cooling, pure 15 crystallized as bright yellow needles which, on reaction with deuterium oxide, gave cis-14 exclusively. (16)Evnin, A. B.; Seyferth, D. J. Am. Chem. SOC.1967, 89, 952. (I 7) Levin, G.;Janur-Grdzinski. J.; Szwarc, M. J. Am. Chem. SOC.1970, 92, 2268.
(18)Kiindig, E. P.; Perret, C. Helu. Chim. Acto 1981, 64, 2606
Figure 2. Pluton drawing of the molecular structure of 10. with the adopted atom labeling. Hydrogen atoms were omitted for clarity.
X-ray Crystal Structures. Surprisingly, the X-ray crystal determinations of compounds 4, 10, and 15 revealed all three of them to be tetrameric clusters; their structures are depicted in Figures 1-3, respectively; bond lengths and angles are given in Tables 1-111. In organomagnesium chemistry, only one X-ray crystal structure of a tetrameric cluster is known: (q5-cyclopentadienyl)magnesium ethoxide (17) (Figure 4). This structure consists of a cubane skeleton with magnesium and oxygen occupying the corner^.'^ It can, however, also be described as four magnesium atoms arranged as a tetrahedron, on each face (formed by three magnesiums) of which a &bridging ethoxide group is positioned. In this way the resemblance with the structures of 4, 10, and 15 becomes obvious; they can, likewise, best bedscribed as consisting of a (distorted) tetrahedron of four magnesium atoms with one organic group attached to each of its faces. An important difference resides in the nature of the bridging group. In 17, it (19)(a) Lehmkuhl, H.; Mehler, K.; Benn, R.; Rufinska, A,; Kriiger, C.
Chem. Ber. 1986,119, 1054. (b) Shearer, H. M. M.;Spencer, C. 8.J. Chem. SOC..Chem. Commun. 1966, 194. (c) Ishimori, M.: Tsuruta, T.; Kai, Y.; Yasuoka, N.; Kasai, N. Bull. Chem. SOC.Jpn. 1976, 49, 1165. (d) Mootz, D.;Zinnius, A.; Bottcher, B. Angew. Chem. 1 9 6 9 , 8 / ,398. (e) Coates, G.E.; Heslop. J . A.; Redwood, M. E.; Ridley, D. J. Chem. SOC.A 1968, 11 18.(f) Ashby, E.C.; Nackashi. J.; Parris. G . E. J. Am. Chem. SOC.1975,97, 3162.
Cyclic Bifunctional Organomagnesium Compounds
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Table 111. Selected Bond Distances and Bond Angles for 15 distances (A)
Mg-0(21) Mg-C(7) Mg-C(8)" Mg-C(8)h C(6)-C(7) C(7)-C(8) C(8)-C(9) Mg-Mg" Mg-Mgh
2.027(8) 2.1 78( I O ) 2.265(9) 2.261(11) 1.519(14) 1.354(14) 1.480(15) 3.045(5) 3.338(5)
anales (dee)
O(2 1)-Mg-C(7) O(2 1)-Mg-C(8)" O(2 1)-Mg-C(8)* C(7)-Mg-C(8)" C( 7)-Mg-C(8)' C(E)"-Mg-C(8)* Mg*-C( 8)-Mge C(6)-C(7)-Mg C(8)-C(7)-Mg C(6)-C(7)-C(8) C(7)-C(8)-C(9)
I 13.7(4) I06.4(4) 106.8(4) 106.3 (4) 1 1 1.6(4) 1 1 1.9(4) 84.6(3) 123.0(7) 1 1 1.0(6) 126.0(9) 122.4(9)
a Indicates symmetry operation y , 1 - x , 1 - z. Indicates symmetry operation 1 - x , 1 - y , z. Indicates symmetry operation 1 - y , x , 1 - z.
W
Figure 3. Pluton drawing of the molecular structure of 15, with the adopted atom labeling. Hydrogen atoms were omitted for clarity. Table I.
Figure 4. Structure of (CpMg0Et)r (Cp = qs-cyclopentadienyl).19~
Selected Bond Distances and Bond Angles for 4 distance (A)
Mg-0 Mg-C(8)* Mg-C( 1) Mg-C(l)" C(I)-C(2) C(I)-C(9) C(2)-C(3) C(3)-C(4) C(4)-C(IO) C(5)-C(6) C(5)-C(IO) C(6)-C(7) C(7)-C(8) C(8)-C(9) C(9)-C(IO) Mg-Mg" Mg-Mgh
2.060(3) 2.142(5) 2.271 (5) 2.267(5) 1.367(8) 1.455(7) 1.419(8) 1.302(9) 1.418(IO) 1.334( 12) 1.443(9) 1.418( IO) 1.382(8) 1.400(8) 1.446(8) 3.203(2) 3.430(2)
angles (deg)
O-Mg-C(8)* 0-Mg-C(I) 0-Mg-C( I)' C(I)-Mg-C(8)* C(I)-Mg-C(l)" C(8)"-Mg-C(If) Mg-C(l)-Mgh C(2)-C(I)-C(9) C(l)-C(2)-C(3) C(2)-C(3)-C(4) C(3)-C(4)-C(lO) C(6)-C(5)-C( 10) C(S)-C(6)-C(7) C(6)-C(7)-C(8) C(l)-C(9)-C(8) C(4)-C( lO)-C(9) C(4)-C(IO)-C(5)
li Indicates symmetry operation y 5/4 - x , symmetry operation '14 - y , ' 1 4 x , 114 - z.
+
l05.05( 19) 99.96( 16) 98.3(2) 112.06(19) 113.4(2) 123.55(19) 89.80(18) 117.2(5) 123.6(5) 121.0(6) 119.8(6) 1 22.5(6) 118.1(6) 125.2(6) 120.0(4) 121.4(5) 122.7(6) - z. Indicates
Table 11. Selected Bond Distances and Bond Angles for 10 distances (A)
Mg(l)-O(l) Mg( 1)-C(6) Mg(l)-C(7) Mg(l)-C(7)" Mg(2)-0(2) Mg(2)-C(l) Mg(2)-C( I)" Mg(2)-C(8)" C( 1 )-C(6) Mg(l)-Mg(l)" Mg( 1)-Mg(2) Mg(lbMg(2)" Mg(2)-Mg(2)"
2.041(4) 2.1 71(5) 2.273(6) 2.291(5) 2.031(4) 2.314(6) 2.237(6) 2.139(5) 1.418(8)
2.804(2) 3.305(3) 3.548(3) 2.841(2)
anales (des)
O(I)-Mg(l)-C(6) O( I)-Mg( l)-C(7) O(I)-Mg(l)-C(7)" C(6)-Mg(l)-C(7) C(6)-Mg(l)-C(7)" C(7)-Mg(l)-C(7)" 0(2)-Mg(2)-C(I) 0(2)-Mg(2)-C(I)' 0(2)-Mg(2)-C(8)' C(I)-Mg(2)-C(l)" C( I)-Mg(2)-C(8)" C ( I)"-Mg(2)-C(8)' C(2)-C( l)-C(6) C( I)-C(6)-C(5) Mg( I)-CG')-Mg( 1 )" Mg(Z)-C(I kMg(2)''
112.5(2) 108.4(4) 106.3(2) 109.8(2) 116.3(2) 102.9(2) 102.3(2) 113.1 (2) 1 1 1.0(2) IO 1.2(2) l20.0(2) 108.9(2) 118.4(5) I16.5(5) 75.8(2) 77.2(2)
" Indicates symmetry operation ' 1 2 - x , y , -z. is an alkoxide; alkoxides are well known for their tendency to form clusters and similar types of associated species.19" In 4,10, and 15, bridging is achieved by (formal) dicarbanions. To our knowledge, this type of purely carbon-bonded, tetrameric organomagnesium clusters has not been encountered previously. The structures of 4, 10, and 15 can also be looked upon as
.g bR2
..fi
IO
'5
Figure 5. General bonding scheme of 4, 10, and 15 (only one organic group shown).
consisting of two dimeric units, connected by p2-bridgingcarbon atoms. In this description, two eight-membered rings in 4 and two six-membered rings in 10 and 15 are thus connected. The connection of two dimers may well be the genesis of the tetramers, and this is confirmed by several aspects of the structures, such as the different magnesium-magnesium distances; however, for the sake of simplicity, we choose to describe these structures as being derived from magnesium tetrahedrons. The structure of a tetrameric cluster is schematically represented for one organic group in Figure 5 . The organic group is bonded to the three magnesium atoms of one tetrahedral plane via two carbon atoms; one carbon atom is bonded via a magnesiumxarbon single bond and the other is bridging in a 1 2 fashion over two magnesium atoms by a 3-center, 2-electron bond (cf. the r3-bridging of ethoxide groups in 17). In the following, the shorthand notation $-(u,p2) will be used to describe this type of bonding of the dicarbanionic ligand. The magnesium4arbon bonding distances in 4,10, and 15 are in reasonable agreement with similar ones reported for normal, monovalent organomagnesium compounds. Our Mg-C single bonds vary from 2.14 to 2.18 A; values of 2.13 to 2.19 A have been reported for diarylmagnesium compounds.*O A few diarylmagnesium compounds containing bridging aryl groups are also known.21 The values found for the Mg-C p-bond distances in these compounds correspond to those found in 4, 10, and 15 (2.24-2.31 A). The Mg-C,-Mg angles are slightly different for the three complexes 4, 89.8(2)'; 10, 77.2(2)/75.8(2)'; and 15, 84.6(3)'. (20) Markies, P. R.; Akkerman, 0.S.; Bickelhaupt, F.; Smeets, W. J . J.; Spek. A. L. Ado. Orgonomer. Chem. 1991.32.147 and referencescitedtherein. (21) (a) Markies, P. R.; Schat, G.;Akkerman, 0. S.; Bickelhaupt, F.; Smeets. W . J . J.; van der Sluis, P.; Spek, A. L. J . Organomef. Chem. 1990, 393, 315. (b) Thoennes, D.; Weiss, E. Chem. Ber. 1978, 1 1 1 , 3726.
2812 J. Am. Chem. Soc., Vol. 115, No. 7, 1993
Tinga et al.
Figure 8. Schematic representation of a divalent organic group on top of one face of a tetrahedron of magnesium atoms. (a)
2
(b)
Figure 6. Structures of dimeric organomagnesium aggregates. (a) @tolyl2Mg)z (18). (b) R ' , R2 = methyl; R 1 = methyl, RZ = cyclohexyl.
CZ"
Figure 9. Two possible arrangements of four divalent organic groups bridging a tetrahedron of magnesium atoms. Figure 7. Comparison of tetrameric organomagnesium clusters with tetrameric organolithium clusters.
An important feature of the structures of 4, 10, and 15 is the coordination of the magnesium atoms, which is essentially the same for all magnesiums in the three structures. They have a pseudotetrahedral coordination to three carbons-one of which is single bonded and two are bridging-and only one T H F molecule, while in simple organomagnesium compounds, tetracoordinate magnesium is coordinated to two ether molecules. To simplify the discussion of this coordination mode, the following notation will be used in which the ligating atoms are listed, and for the carbon atoms, the nature of the bond to magnesium is indicated OC,(C,)2. In this notation, the normal coordination mode of R2Mg*(OR2)2 is represented as 02(C,)2. Only one similar OC,(C,)2 coordination has been reported, thedimeric [(p-tolyl)2MgTHF]2 (18) (Figure6a). This complex cocrystallized in a 1:l ratio with the monomeric form (pt01yl)~MgTHF~ (which has the normal coordination mode 0 2 (CU)2).2la Furthermore, two structures with a NC,(C,)2 coordination mode have been published22(Figure 6b). These complexes, together with 17, are the only examples of structurally identified organomagnesium compounds containing no metals other than magnesium which show aggregate formation in combination with coordination of ethers. Higher aggregates are typically formed only in the absence of Lewis bases, for instance (MezMg),,23and ( P h 2 M ~ ) " ,both ~ l ~ ofwhich have thecoordination mode (Cp)4. The reluctance of organomagnesium compounds to form aggregates is in sharp contrast with the behavior of organolithium compounds, where tetrameric and higher aggregates are common, whereas smaller ones are an exception.24a There is an interesting resemblance between the structures of tetrameric alkyllithium compounds and those of 4, 10, and 15. The alkyllithium compounds consist of a tetrahedron of lithium atoms with an alkyl group p3-bridging three l i t h i ~ m sroughly ,~~~ similar to the structures of our organomagnesium clusters (Figure 7). In thelithiumcase, a monocarbanion bridges a (Li+)3triangle in a p3 fashion, where in 4, 10, and 15, a dicarbanion bridges a (Mg2+)3triangle in the v2-(u,p2)mode. This stoichiometric correspondence of (Li+R-)4versus (Mg2+R2-)4 must be one of the factors governing the cluster formation of 4, 10, and 15, but other electronic and steric factors are of importance as well. Aggregate formation of organometallic compounds is generally caused by the polarity of these (22) Bogdanovic,B.; K0ppetsch.G.;Kriiger.C.; Mynott, R. 2.Nafurforsch. 1986. 41 b, 6 1 I.
(23) Weiss, E. J . Organomef. Chem. 1965, 4, 101. (24) (a) Setzer, W. N.; Schleyer, P. v. R. Adu. Organomel. Chem. 1985, 24, 353 and references cited therein. (b) Schade, C.; Schleyer, P. v. R. Adu. Organomef. Chem. 1987, 26, 169.
c o m p o ~ n d s . ~Since ~ ~ - ~organomagnesium compounds are less polar than organolithiums, they havean inherently lower tendency to form aggregates. Furthermore, magnesium is a stronger Lewis acid than lithium and therefore has a greater preference for hard Lewis bases, such as T H F molecules. This explains why in organomagnesium chemistry, 02(Cu)2coordination is, in general, more stable than OC,(C,)2 and (CJ4 coordination; monomers will therefore be more stable than dimers such as 18. In solution, however, monomer4imer equilibria exist, as is for example illustrated by the case of (p-tolyl),Mg (vide supra).21a Only in special cases, higher aggregates are formed. Thus in 17, the ethoxide anions, combining p3-bridging ability19with hard Lewis base character, lead to tetramerization. We feel that in 4, 10, and 15, other factors are decisive. With the exception of dimeric 4, monomeric or dimeric species are unlikely to be formed because the small C-Mg-C bond angles in such species would cause excessive strain.20 For higher aggregates and for dimeric 4, models show that the 02(C,)2 coordination of the two magnesiums bonded to the same organic group (1,8-naphthalenediyl, o-phenylene, or cis-diphenylvinylene) would result in overcrowding, due to the proximity of the magnesiums with their two ether ligands. Aggregate formation, on the contrary, yields species that are less crowded, because only one T H F molecule per magnesium is necessary to achieve tetracoordination. Finally, it should be emphasized that the specific geometric features of the three dicarbianions are also important. Their rigidity as well as the short distance between the two carbanionic carbon atoms in 4,10, and 15 are prerequisite for the v2-(a,p2)-bridgingmode, as they provide a good "fit" of the dianion on top of the Mg3 triangle. Not directly evident from the PLUTON drawings (Figures 1-3) is the relation between the four organic groups spanning the tetrahedron of magnesium atoms. Therefore, the schematic representation of Figure 8 is introduced. The organic groups are represented by their projection (bold line) on the face of the magnesium tetrahedron over which they are positioned. When the bold line ends at the corner of a triangle, it indicates a Mg-C u-bond; when it ends in the center of an edge of the tetrahedron, it indicates a p carbon atom bridging between the two magnesium atoms connected by that edge. Taking into account that each magnesium has a OC,(C,)2 coordination mode, two arrangements are possible when four groups are introduced (Figure 9). They differ in symmetry, one possessing C2cand the other S4symmetry. Differences between the two arrangements are particularly important for the Mg-Mg relationships. The C2rarrangement has two pairs of magnesiums (Mg( 1)-Mg(2) and Mg(3)-Mg(4)), each pair being p-bridged by two carbon atoms; this results in two four-membered Mg2C2 rings. The other four pairs of magnesiums (Mg(1)-Mg(3), Mg-
J. Am. Chem. Soc.. Vol. 115, No. 7, 1993 2813
Cyclic Bifunctional Organomagnesium Compounds (1)-Mg(4), Mg(2)-Mg(3), and Mg(2)-Mg(4)) do not share a p-bridging carbon atom. In the S 4 arrangement, there are four pairs of magnesiums that share one p-bridging carbon, (Mg(l’)-Mg(2’), Mg( 1’)-Mg(4’), Mg(2’)-Mg(3’), and Mg(3’)-Mg(4’)) andtwo pair sthat sharenone(Mg( l’)-Mg(3’)and (Mg(2’)Mg(4’)); there are no four-membered Mg2C2 rings. Actually, both arrangements are realized: 4 and 15 have the &-like and 10 has the &like arrangement. The structure of 10 possesses only approximate C2csymmetry. It has, in fact, C2 symmetry, because the bridging of the phenylenes is unsymmetrical, i.e., the +bridging carbon atom is closer to one magnesium than to theother (2.237(6) vs 2.314(6) and 2.273(6) vs 2.291(5) A, respectively, for the two independent phenylenes). In the structure of 10, two four-membered Mg2C2 rings are present (Mg(1)-Mg(1’) and Mg(2)-Mg(2’), see Figure 2). The MgMg distance in these rings is very short (2.804(2) and 2.841(2) A, respectively) when compared to the other Mg-Mg distances in 10 (3.305(2)-3.548(2) A). It is evident that this leads to a considerable distortion of the tetrahedron. Such a distortion is also present in the structures with Sd symmetry. In 4, the MgMg distances are 3.203(2) A (one bridging 1,8-naphthalenediyl) and 3.430(2) A (unbridged). In 15, the corresponding values are 3.046(5) and 3.338(4) A, respectively. The tetrahedron of magnesiums in 4 is larger than that in 15, which is obviously a reflection of the two different carbon skeletons, in particular of the larger distance between the two carbanionic centers in 4. The preference of a particular compound for one of the two arrangements is not obvious. In solution, there probably is a fast equilibrium between both arrangements, as evidenced by the equivalence of the u- and p-bridging carbon atoms in the 13C N M R spectra (vide infra), indicating that both arrangements are very close in energy. A priori, a conceivable factor might have been the number of carbon atoms separating both magnesium functionalities in one organic group. However, this can be easily dismissed, as in 10 and 15 the magnesium atoms are bonded to adjacent carbon atoms, whereas in 4 they are separated by three carbon atoms, while the arrangements adopted by 10 and 15 are different (C2c and S4, respectively), whereas those of 4 and 15 are not. Possibly, the bulkiness of the organic group may play a role: 4 and 15, containing larger organic groups, have the S 4 arrangement, while 10, with the smaller o-phenylene group, has the C2, arrangement. Two metal substituents in close vicinity are obviously causing considerable steric hindrance to each other. Thus, while 10 is easily derivatized with chlorotrimethylstannane to give the diand monosubstitution products in a ratio of 80:20,4, under the same conditions, yields a ratio of di-, mono-, and unsubstituted products of 22:67: 1 1. Similarly, 6 and related compounds reveal serious distortions due to steric hindrance.lO Obviously, 1,3disubstitution with (more or less) parallel orientation of the 1,3bonds as in 4 causes more crowding than 1,2-disubstitution with angles of approximately 120°; for this reason, 4 is more crowded than 10. The higher degree of congestion in 15 as compared to 10 can be ascribed to the two phenyl substituents at the central double bond in the former. The observation that the less crowded situation as in 10 goes along with the CzOarrangement suggests that its doubly p-bridged, four-membered Mg& rings are inherently more stable than the “open”, alternating singly r-bridged rings in the S4 arrangement; on the other hand, the Mg2C2 rings entail closer proximity of the bridging groups and will be unfavorable when the bulk of these bridging groups increases. In view of the slight energy differences between the two different arrangements, crystal packing effects may be another important factor. In this regard, it may be relevant that a large amount of free, disordered T H F molecules is present in the crystals of theS4arranged 4 and 15. These molecules seem to be necessary for the stability of the crystal; this certainly holds for crystals of 4, as they collapse in a THF-free environment, either in vacuum
4 :
a = 115.2(5)
10 : a’= 116.5(5)/117.0(5) p’ = 118.4(5)/118.2(5)
p = I17.2(5)
Figure 10. Effect of magnesium substitution on endocyclic angles.
Figure 11. Bond distances fragments of (1O.THF)d.
(A)
Figure 12. Bond distances (15TH F)4.
(A) in
in the two independent o-phenylene
the cis-diphenylene fragment of
or under a nitrogen atmosphere. In contrast, the crystals of 10 are completely free of nonbonded THF molecules; apparently, the crystal packing is quite different. It is at present unclear which of these factors is dominant. The organic fragments in the crystalline complexes show some interesting features. The endocyclic C-C(Mg)-C bond angles CY and B (see Figure 10) are distinctly smaller than the 120° usually found in the unsubstituted aromatics. This is a common feature for metalated aromatic compounds.25 The angles a t bridging carbon atoms (0 and 8’) are slightly larger than those involving u-bonds to carbon (CYand a’). The carbon-carbon bond distances within the o-phenylene fragments of 10 are influenced by the substitution (Figure 11). The C(l)-C(2) bond distance is noticeably longer (about 1.42 A) than the other C-C bond distances; the latter are close to that in benzene itself (1.397 A26) with the exception of the bonds opposite to C( l)-C(2), which are remarkably short (average 1.36 A). Two factors may be responsible, and both are a consequence of the fact that carbon atoms bonded to magnesium atoms bear a considerable negative charge: the charge as such will lead directly to electrostatic repulsion and indirectly to rehybridization of the carbon atoms such that the C-Mg bond will have more s-character and the intraannular C - C bonds more p-character; this is also in line with the small intraannular angles (vide supra). The carbon-carbon distances in the benzene rings of 10 do not support the concept that C(2) is tetracoordinate in the sense that they resemble those in the Wheland complex of aromatic electrophilic substitution; rather, like in other bridging alkyl or aryl groups, the Mg-C(Z)-Mg bond is of the 3-center, 2-electron type involving only the carbanionic u-orbital of C(2). An interesting detail of the structure of 15 involves the C(6)C(7) and the C(8)-C(9) bond distances, which differ considerably: the bond of C(9) to the bridging C(8) is shorter (Figure 12). Also, the angles between the planes of the phenyl groups at C(7) and C(8) and the central double bond plane C(6)-C(7)C(8)-C(9) are 73 and 41°, respectively. Both features suggest that a more efficient benzylic type 1-overlap exists between the (25) (a) Thoennes, D.; Weiss, E. Chem. Ber. 1978, I I I , 3726 and references cited therein. (b) Harder, S.Thesis, Rijksuniversiteit Utrecht, 1990. (26) Ermer, 0.Angew. Chem. 1987,99,791 and references cited therein. (27) (a) van Vulpen, A,; Coops, J . Rec. Trau. Chim.Pays-Bas 1967.85, 203. (b) van Vulpen, A. Thesis, Vrije Universiteit, Amsterdam, 1967. (c) Freijee, F. J. M . Thesis, Vrije Universiteit, Amsterdam, 1981.
2814 J . Am. Chem. SOC.,Vol. 115, No. 7, 1993 Table IV.
Degree of Association of 4 and 10 Sdh 0.044 0.113 0.172 0.229 0.291 0.350
1
I
111
111
10
4
[Mglf 5.21 10.42 15.63 20.84 26.05 31.26
Tinga et al.
Sib'
id
0.229 0.459 0.688 0.917 1.146 1.375
5.20‘ 4.06 4.00 4.00 3.94 3.93
[Mglf 7.12 13.69 19.77 25.41 30.65
Sah 0.079 0.152 0.228 0.296 0.345
Sthl 0.318 0.611 0.882 1.133 1.367
id 4.02 4.02 3.87 3.82 3.96
“ [Mglr = formal concentration of magnesium in mmol L-I (Le., concentration if all particles were monomeric, containing one Mg atom). S,= apparent rateof the evaporation in mm h- I. S1h = theoretical rate ofevaporation (in mm h I) = [MglrS,, whereS, (in mm h-I mmol-I L-I) is the standard rate of evaporation found by calibration of the apparatus with triphenylmethane, S, (296 K) = 0.0440 mm h I mmol-’ L-I. Association number i = &,/Sa. e The first value is often unreliable due to the low concentration (ref 2 7 ) . / A s in ref c, the standard rate of evaporation found by calibration of the apparatus with triphenylmethane just before the experiment: S,(296 K) = 0.0446 mm h-’ mmol I L-I.
Figure 14. Rotation of an organic group.
CZ” s4 Figure 15. Interconversion of the arrangements by two rotations.
Figure 13. Numbering adopted for the discussion of the N M R spectra.
phenyl group a t C(8) and the olefinic bond C(7)-C(8), resulting in a slight lengthening of this bond and shortening of the C(8)C(9) bond. Structure in Solution and NMR Spectroscopy. The novel type of crystal structure found for 4, 10, and 15 immediately raised questions about their structure in solution. The appreciable solubilityofboth4and lOinTHF(ca.0.l M atroomtemperature) allowed the investigation of their structure in T H F solution by association measurements and by N M R spectroscopy. The degrees of association of 4 and 10 in T H F were measured by the method of stationary isothermal distillation. Both compounds were found to be tetrameric in THF solution at room temperature (4, association number i = 3.98; 10, i = 3.92). The data for the measurements are collected in Table IV. Assuming that the tetrameric structures of 4 and 10 are the same in solution as in the crystalline state, this should have certain consequences for their N M R spectra. In the crystal, the organic groups are unsymmetric due to the fact that one carbon atom (C( 1) in Figure 13) is single bonded to magnesium and the other one (C(1’)) is p-bridging between two magnesiums (note the different numbering adopted for this part of the discussion). As a consequence, C( 1) and C(l’), but also the carbon atoms C(n) and C(n‘), as well as the protons they carry, should experience different chemical surroundings, and therefore, in principal, they should have different chemical shifts. However, such differences were not observed (see Experimental Section); the compounds gave spectra as expected for a symmetrically 1&disubstituted naphthalene and a symmetrically 1,2-disubstituted benzene, respectively. In the IH broad-band decoupled I3C N M R spectrum, signals assignable to C( 1) and C( 1’) are sharp singlets; line broadening relative to other signals was not observed. Measurements at low temperatures (as far as -80 “C) for 10 did not result in any decoalescence phenomena; such measurements were impossible for 4 because it precipitated on lowering the temperature. We conclude that in THF solution there must be a mechanism leading to exchange of C ( l ) and C(1’) (or C(n) and C(n’), etc.) at a rate which is fast on the N M R timescale. An intermolecular exchange, which is usually rapid for monovalent organomagnesium compounds, is not likely for the divalent species at hand
because of their stable tetrameric aggregation. An intramolecular exchange reaction may seem complex at first sight, since the conversion of a Mg-C a-bond to a Mg-C p-bond must result in complex changes throughout the cluster. The most simple way of C( 1)-C( 1’) exchange in one organic group involves rotation of this group relative to the face of the tetrahedron above which it is positioned (Figure 14); by this operation, a u-bonded carbon (C,) becomes p-bridging, while the p-bridging Cb becomes a-bonded. From the representation of the structure by use of the projection of the organic group (cf. Figures 8 and 9), it is obvious that a rotation by only 60’ is sufficient to achieve this exchange. A distinction between a concerted process and a mechanism in which these changes of the Mg-C bonds occur stepwise, e.g., first exchange of one of the bridging bonds of C,, is not a priori possible. Both processes involve only a minor movement of atoms, as the nonbonding distances C( 1)-Mg(2), C(1)-Mg(3), and C( 1’)Mg( 1) are rather small. If one considers the tetrameric cluster as a whole, it is obvious that the rotation of one of the organic groups cannot occur without simultaneous rotations of other groups in the same cluster in order to maintain tetracoordination (OC,(C,)2) for each magnesium. The conversion of a arranged cluster into another one of CZ,symmetry requires rotation of alljour organic groups. The same holds for an &-S4 conversion. A conversion of a C2” arranged cluster into one Of S4 symmetry requires only two of the organic groups to rotate (Figure 15). This interconversion between both arrangements results in the C( I) 2.5u(I)] formula mol wt crystal system space group a,c (A) V(A3)
+
no. refined parameters weighting scheme final R, R,, S (A/.)." in final cycle min and max resd d (e/A3)
Refinement 146 w = l . O / [ d ( F ) + 0.000 201Fzl 0.068.0.083, 2.86 0.0287 -0.18,O. 19
with anisotropic thermal parameters, and H-atoms were refined with one common isotropic thermal parameter [U= 0.135(7) A2]. At this stage (R = 0.1 5 5 ) , a difference Fourier map showed various features of about 1 eA-' located in four symmetry-related channels: parallel to the a-axis [at y = l / 4 . z = l / 4 and y = '/4. z = 3/4] and to the b-axis [at x = 0; z = I/']. N o discrete T H F solvent model could be z = 0 and x = fitted in the electron density within these channels. The BYPASS procedure3' was used to take the electron density in the channels into account in the subsequent structure factor and Fourier calculations. A total electron count of 814 was found for the four channels with a volume of 2978 A', which is indicative of a total of 20 T H F molecules in the unit cell (five molecules of T H F in each channel). The averagevolume of one T H F molecule in the channels is 149 A), this is in reasonable accordance with the volume of one T H F molecule in the liquid phase at 293 K (136 A'). Weights wereintroduced in the final refinement cycles,convergence was reached at R = 0.068. R, = 0.083. Crystal data and numerical details of the structure determination are given in Table V. Final atomic coordinates and equivalent isotropic thermal parameters are listed in TableVI. Neutralatomscatteringfactors weretaken from32andcorrected for anomalous dispersion.J3 All calculations were performed with SHELX7634and the EUCLID package3s (geometrical calculations and illustrations) on a Micro VAX cluster. Synthesis of ePhenylenemagnesium (IO). o-Phenylenemercury (7* 4.46 g, 16.1 mmol) and magnesium (3.65 g, 150 mmol) in T H F (180 mL) were stirred for 2 weeks at room temperature and for 10 h at 70 OC. A pale yellow solution with a fine black precipitate was obtained. The solution was separated from the excess magnesium and the black precipitate by careful decantation. Titration of an aliquot (HCI, EDTA) indicated formation of 10 in a yield of 85%. Crystallization by slowly cooling this solution afforded colorless crystals ( I 1.0 mmol, 68% isolated yield; yields determined by titration). 10.(THF).: ' H N M R ([2Hg]toluene, 250 MHz, ref [2H,]toluene = 2.03) b 8.12 (dd, ' J = 5.0 Hz, 4J = 3.2 Hz, 2 H), 7.23 (dd, 'J = 5.0 Hz, 4J= 3.3 Hz, 2 H), 3.24 (bs, 8 H), 1.2 (bs, 8 H); ' H N M R (200 MHz, [2H8]THF,ref [2H,]THF = 1.75 ppm) 6 7.67 (dd, ' J = 5.0 Hz, 4J = 3.2 (3 1 ) Van der Sluis, P., Spek, A. L. Acra Crysrallogr. 1990. A46, 194. (32) Cromer, D. T.; Mann, J . B. Acra Crysrallogr. 1968, A24, 321. (33) Cromer, D. T.; Liberman, D. J. Chem. Phys. 1970, 53. 1891. (34) Sheldrick, G. M. SHELY76. Crystal structure analysis package; University of Cambridge: England, 1976. (35) Spek, A . L. In Compuratioaal Crysrallography; Sayre, D., Ed.; Clarendon: Oxford, 1982; "the EUCLlD package", p 528.
2816 J . Am. Chem. SOC.,Vol. 115, No. 7 , 1993
Tinga et al.
Table VI. Final Coordinates and Equivalent Isotropic Thermal Parameters of the Non-Hydrogen Atoms for 4
atom
X
Y
2
Mg 0 C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(I I ) C(12) C(13) C(14)
0.553 81(11) 0.5837(3) 0.6171(4) 0.7076(4) 0.7592(4) 0.7216(5) 0.5818(6) 0.4929(6) 0.4426(4) 0.4783(4) 0.5718(4) 0.6273(5) 0.6114(5) 0.5923(6) 0.5352(5) 0.5542(5)
0.64403(11) 0.5095(2) 0.6471(3) 0.6244(4) 0.5623(4) 0.5222(4) 0.4990(4) 0.5148(5) 0.5758(4) 0.6206(3) 0.6025(3) 0.5395(4) 0.4335(5) 0.3473(4) 0.3732(5) 0.4719(4)
0.09504(4) 0.079 66(10) 0.154 57(14) 0.147 79(15) 0.170 97(19) 0.200 54(19) 0.242 27(19) 0.250 43(19) 0.226 30(18) 0.194 59(14) 0.186 89(14) 0.209 51(17) 0.1034(2) 0.0818(2) 0.048 45(18) 0.044 06(17)
L1
U(eq) =
'/3
U(eqla [Az] 0.0640(6) 0.0813(16) 0.069(2) 0.079(2) 0.094(3) 0.095(3) 0.109(3) 0.1 13(3) 0.094(3) 0.069(2) 0.0653(19) 0.087(3) 0.135(4) 0.151(4) 0.109(3) 0.099(3)
of the trace of the orthogonalized U matrix.
Table VII. Crystal Data and Details of the Structure Determination for 10
Crystal Data C4oH4aMg404 690.04 monoclinic I2/0 (No. 15) 17.071(3), 11.877(1), 18.809(1) 99.97( 1) 3756.0(6) v ('4') Z 4 (g cm 9 1.220 F(000) 1472 1.3 p(Mo K a ) (cm I ) crystal size (mm) 0.20 X 0.50 X 0.50 Data Collection T (K) 294 radiation Mo K a (Zr-filtered), 0.710 73 A O,,,,,O,,.,, (de@ 1.4, 26.5 scan type w/20 scan (deg) 0.90 + 0.35 tan 0 hor and vert aperture (mm) 4.00, 6.00 reference reflections -1 2 -1, -2 -1 -3 data set h: -21:O; k: 0 ~ 1 4I: ; -23123 total unique data 3921,3591 observed data 1990 [I> 2.5a(1)] Refinement no. of refined parameters 220 weighting scheme w = 2.3950/[u2(F) + 0.001 3 0 4 P l final R, R,, S 0.0663,0.0916, 2.24 max and av shift/error 0.09,O.Ol min and max resd d (e/A3) -0.18,0.19 formula mol wt crystal system space group a, b, c (A) P (deg)
Hz, 2 H), 6.74 (dd, ' J = 5.0 Hz, ' J = 3.3 Hz, 2 H); ''C N M R (['HalTHF, 62.9 MHz, ref [?H7]THF = 67.4 ppm) 6 189.1 (bs, C(1,2), 140.6 (dd lJ(CH) = 150 Hz,3J(CH) = 5 Hz, C(3,6)), 124.3 (d, ' J ( C H ) = 150 Hz, C(4,5)), 66.2 (bt, IJ(CH) = 140 Hz, T H F C and x = I/?, y = 0. N o discrete solvent model could be fitted in this density. The BYPASS procedure)' was used to take the electron density in this hole into account in the refinement. An electron count of 173 was found for both channels, with a total volume of 626 A', which is indicative of a total of four T H F molecules in the unit cell. The atomic volume of the nonhydrogen atoms (31 A3) is in reasonable accordance with that found in the liquid phase (27 A3). In the final cycles of full-matrix least-squares refinement using SHELX76,34 183 parameters were refined, including an overall scale factor and positional and anisotropic thermal parameters for all non-H atoms. H atoms were included in the refinement on calculated positions riding on their bonded atoms (C-H= 0.98 A) with overall isotropic thermal parameters for the diphenylvinylene group and thecmrdinatedTHFof0.088( 12) and0.20(3), respectively. Final atomic coordinates are listed in Table X. Scattering factors were taken from ref 32 and anomalous-dispersion corrections from ref 33. Geometric calculations were performed with the EUCLID package.35 All calculations were performed on a MicroVAX-11. Association Measurementsof 6and 12. The association measurements of4and 10wereperformed usingthe techniqueof isothermaldi~tillation.2~ The compounds were crystallized and washed with cold T H F before use. Relevant data are given in Table IV.
+
+
Acknowledgment. X-ray data were kindly collected by A. J. M. Duisenberg. We thank Shell Research B.V. for financial support (M.A.G.M.T.). This work was supported in part (E.H., H.K., W.J.J.S., and A.L.S.) by the Netherlands Foundation for Chemical Research (SON) with financial aid from the Netherlands Organization for the Advancement of Pure Research (NWO). Supplementary Material Available: Thermal motion ellipsoid plots, tables of anisotropic thermal parameters, bond distances, and bond angles for 4 and 15 (1 1 pages); listings of observed and calculated structure factors (20 pages). Ordering information is given on any current masthead page.
